Genetically modified crops are causing a decline in healthy monarch butterfly migrations between the U.S. and Mexico, finds new data conducted by researchers at the University of Guelph in Canada.

Milkweed, the main food for monarch butterflies, is targeted by Monsanto’s Roundup, the glyphosate-based herbicide that works in tandem with genetically modified crops including GMO corn and soy, where milkweed is often found. Illegal logging in Mexico, is also linked to issues with monarch butterfly migrations and the severe population decline.

According to the research, published in the current issue of the Journal of Animal Ecology, the number of milkweed plants in the U.S. corn belt, where most monarchs breed, “has fallen 20 per cent over the past few decades,” reports Canada’s CBC News. “This past winter, the number of monarch butterflies wintering in Mexico fell to its lowest since 1993, when records first started being kept, the World Wildlife Fund and Mexico’s Environment Department reported in January.”

Both the World Wildlife Fund and Mexico’s Environment Department blame the widespread planting of genetically modified crops for the loss of milkweed as the main source of declining monarch butterfly populations.

“The leaves of the milkweed plant are the only place that monarchs lay their eggs and the only food that monarch butterfly caterpillars will eat,” reports CBC.

“It’s a massive number of milkweeds — about 1.5 billion milkweed plants,” Tyler Flockhart, a postdoctoral researcher at the University of Guelph who led the research, told CBC.

Many monarch butterfly populations east of the Rocky Mountains breed in the U.S. corn belt—in between Kansas and Ohio and from Missouri up to North Dakota.

According to Flockhart’s research, “a huge quantity” of milkweed would need replanting throughout the U.S. in order to help monarch butterfly migrations to return to healthy levels. Toxic to humans and some animals, milkweed is often treated as a nuisance, making it even more of a challenge for the monarchs to recover.

Jill Ettinger is a Los Angeles-based journalist and editor focused on the global food system and how it intersects with our cultural traditions, diet preferences, health, and politics. She is the senior editor for sister websites OrganicAuthority.com and EcoSalon.com, and works as a research associate and editor with the Cornucopia Institute, the organic industry watchdog group. Jill has been featured in The Huffington Post, MTV, Reality Sandwich, and Eat Drink Better. Twitter @jillettinger | www.jillettinger.com.

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